Twenty years ago today, the Exxon Valdez ran aground in the Prince William Sound and spilled nearly 11 million gallons of crude oil. Hundreds of miles of Alaska’s coastline were coated in oil, a quarter of a million seabirds died, and one estimate puts local fisheries’ losses at nearly $300 million, reports TIME’s Bryan Walsh.

In 1991, Exxon reached a civil settlement with the federal and Alaska government and agreed to pay $900 million for restoration of the affected area; $180 million of that has gone to research. At the same time, Exxon funded its own research efforts. I’m sure few of our readers will be surprised to hear that the Exxon-funded researchers’ conclusions often differed from those of government researchers. Lila Guterman writes in Science:

For example, one of the largest efforts has been to track the fate of the oil remaining in the sound years after the spill. In 2001, a team led by Jeffrey Short, a chemist then with NOAA, randomly sampled 91 beaches in the oiled parts of the sound, digging 9000 pits. Short estimated that 55,000 liters of oil remained, spread across and underneath 11 hectares of beaches.

David Page, an Exxon-funded chemist at Bowdoin College in Brunswick, Maine, insisted, after conducting his own sampling, that the government estimate was too high. Even though he later came to accept Short’s results, he and others still questioned whether the lingering oil is affecting wildlife. They argue that other sources of hydrocarbon pollution outweigh what little oil remains from the 1989 spill. The remaining oil, says Page, is sequestered. “If it were available to be harming wildlife, it would have been long gone.”

Government researchers challenge those claims. In 2005, Short’s team resampled 10 of the beaches where oil remained in 2001. They reported in 2007 in Environmental Science & Technology that the oil was decaying at just 0% to 4% per year. “It will persist for decades up to a century,” says Short, who retired from NOAA a few months ago and now works for Oceana, a marine conservation group. In another study reported last year in Marine Environmental Research, Short’s team found that biologically active contaminants in the region were predominantly from the oil spill; he also thinks that biomarkers such as a particular liver enzyme reveal that organisms have been exposed to oil.

It’s good to hear that there are a few areas of agreement: According to Guterman, both government and Exxon-funded scientists agree that bald eagles, cormorants, salmon, river otters, and other species have recovered. But government scientists are still concerned about killer whales and sea otters, whose populations are still low in the areas that sustained the most damage. Both scientists and fishermen are particularly concerned about the herring stock, which has collapsed and imperiled many livelihoods. The Seattle Times’ Hal Bernton focuses his article on John Renner, a fisherman from Cordova, Alaska, who had been preparing for the spring herring harvest when the oil spill occurred:

The year after the spill, Renner concluded that something was seriously wrong with the herring inside these pens. Instead of laying their roe in flat sheets across the kelp, the herring deposited the eggs in weird little towers.

In 1991, Renner noticed that some of the herring ring never spawned at all. He cut them open, and found they appeared to have reabsorbed the eggs.

“I had never seen anything like it and was horrified,” Renner said.

A few years after the 1993 crash, there was hope that the herring populations were on the mend. State officials allowed three years of small commercial harvests that ended in 1998 when the herring populations plummeted again.

There have been no herring harvests in the past decade, leaving Prince William Sound fishermen dependent on the vagaries of salmon fishing.

Even when salmon runs have been strong, prices for pinks were often at rock-bottom levels. Many fishermen had financial problems as they struggled to pay off debts for boats and harvest permits.

Bernton reports that many fishermen are collecting damages from Exxon Mobil, but “more than 100 fishermen risk having all or part of their checks claimed by the state of Alaska to pay down debt for permit loans.” Fisherman had to take out these loans after the spill ruined their harvest – and with the herring population failing to rebound, their economic future still looks shaky.